I went back to my sculpey supply because I was selling some of it on ebay, and I found that it had eaten away at my plastic storage drawers!! The clay had been sitting in these drawers undisturbed for about 2 years, and it has eaten holes in my storage drawers and turned them into a gooey mess. Here are some pics.
I am sticking my finger through a hole made by glow in the dark sculpey (it seems like this was the most corrosive):
Another pic of the hole in one drawer. The shiny areas around each piece of clay are melted-ish plastic, it's gooey like clear glue.
Some more melted areas around pieces of clay:
This is so weird! I guess you shouldn't store sculpey in plastic containers because of a chemical reaction?